Multiple hearth furnace



Oct. 31, 1944. w. s. MARTIN 2,361,557

MULTIPLE HEARTH FURNACE Filed March 4, 1942 3 Sheets-Sheet 1 INVENTORWARREN S. MARTIN 2. 24 I1 23 25 1; ATTORNEY Oct. 31, 1944. w. s MARTIN2,361,557

MULTIPLE HEARTH FURNACE Filed March 4. 1942 s Sheets-Sheet 2 INVENTORWARREN s; MARTIN Oct. 31, 1944. I w s R-rm 2,361,557

MULTIPLE HEARTH FURNACE Filed March 4. 1942 3 Sheets-Sheet 3 3Ib 28bWARREN S. MARTIN BY D ATTORNEY and having means for Patented Oct. 31,1944 UNlTED STATES PATENT OFFICE MULTIPLE nmn'rn FURNACE Warren s.Mai-an, Hassapequa, N. r. Application March 4, 1942, SerialNo. 433,274

9 Claims. (Cl. 214-21) This invention relates to improvementsparticularly adapted for use in multiple hearth furnaces of the type inwhich a furnace is divided into compartments between thetop and aplurality of superimposed hearths of which the lowermost may be thebottom of the furnace, and the material deposited on the top hearth isfed downwardly from hearth to hearth by rabbling means acting to feedthe material either inwardly to central discharge means or to peripheraldischarge means, the arrangement of discharge uppermost hearth'of such afurnace in such a manner as to utilize a greater part of the uppersurface of such hearth more efliciently than heretofore. A furtherobject is to providematerial supply means whereby the material to betreated will be fed substantially uniformly to a substantial annulararea. on the hearth so that a. large part of the hearth surface will beused effectively as the rabbling means moves the material to the meansbeing different for adjoining hearths.

More particularly the invention relates to improvements in feeding thematerial to the upper part of the furnace in such a manner that thematerial-receiving surfaces of the uppermost hearth or hearths will beutilized to the greatest advantage.

Heretofore it has been a common practice to supply material to theuppermost hearth through a chute passing through the top of the furnacepreventing the escape therethrough of heated rial be deposited near the"center. of an uppermost hearth having peripheral discharge means oropenings the rabbling means over such hearth will, when operating, actto work the material to the periphery for discharge to the next lowerhearth- It will be evident that the rabbling means not distribute thematerial uniformly around the central part of the uppermost hearth butwill leave a bare portion of the hearth'bounded approximately at itsouter side by a curve extending from a position approximately beneaththe inner side of the chute, in the general shape of an expanding spiraluntil it reaches the peripheral part of the hearth, containing theoutlet means or openings. Obviously such bare portion of the uppermosthearth reduces proportionally the heating capacity of the furnace andmay also result in reduced efliciency of the next-lower hearth due toimproper distribution thereon. A corresponding loss of efliciency wouldalso be encountered if the material were supplied to the Peripheral partof the uppermost hearth and fed toward a central discharge means oropening. A plurality of' supply chutes mightreduce the mute area on theuppermost hearth but might introduce other difliculties.

An important object of the invention is to provide means whereby afurnace hearth or the upper part of a multiple hearth furnace may beused to greater advantage thus increasing the efllciency of the furnace.Another object of the invention is to provide means for feeding materialto the outlet or discharge means associated with such v hearth.

The present invention may be carried out by depositing the material tobe treated on a rotary distributing platform having a substantiallycircular edge and then gradually feeding material over said edge to fallon an annular area on said uppermost hearth. Then the rabbling meanswill distribute the material substantially uniformly over the effectivesurface of the hearth on its way toward the outlet means. Suchuniformity of distribution on the uppermost hearth will also airorgases. If the mate- I tend to produce greater uniformity ofdistribution of material on the next lower hearth, and thereforeincrease the capacity of the furnace by drying material more rapidly.

Other objects, features and advantages will appear upon consideration ofthe following detailed descriptionand the drawings in which:

Fig. iis a vertical section of the upper part of a multiple hearthfurnace comprising an embodiment of the present invention;

Fig. 2 is a horizontal section taken along the line 22-of Fig. 1;

Fig. 3 is a detail partly in section of the arrangement at the centralpart of the furnace top;

Fig. 4 is a vertical-section of a modified form of multiple hearthfurnace involving the present invention;

' Fig. 5 is a horizontal section taken along line 5-5 of Fig. 4; p

Fig. 6 is a vertical section similar to Fig. 4, of a miutiple hearthfurnace embodying a second modified form of the invention? and Fig. I isa section taken along the line 1-1 of Fig. 6.

Referring to the drawings. there is illustrated in Fig. 1 a verticalsection of the upper part of a vertical multiple a substantially roundperipheral wall II, a top H, an uppermost hearth l3, having at itsperiphery outlet or discharge means preferably comprising a plurality ofoutlets or drop holes ll hearth furnace ,ll having may drop to the nextlower hearth (not shown).

The first two hearths I3 and I5 are usually used for drying purposes andhearths below hearth 15 are ordinarily used forburning the materialdried in the compartments above the two dryinghearthsl3andl5.

Material after deposit on the hearth maybe distributed over the hearthsand moved toward the outlets by rabbling means which may comprise arotary vertical shaft ll passing through the central opening ii ofhearth l5 with a substantial space to spare, and passing throughsuitable gas seals at the center of the uppermost hearth l3 and at thecenter of the furnace top 12. Above the hearths l3 and 15 are radialarms approaches the circular outer edge of the platform where it issubstantially a continuation of the outer wall of the chute. Thematerial on such annular area of the hearth i3 is in position to beacted on by the rabbling means and worked over to the peripheral outletsor drop holes 14, the supply of material to the various drop holes beingfairly uniform thus assuring it carried by the shaft 11 and providedwith downwardly projecting members or blades IS with their forwardsurfaces so inclined that those above the hearth 13 move material to theperiphery and those above hearth 15 move material to the centralopeningl6.

- The description thus far might apply to many furnaces heretofore inuse. In such prior furnaces it was a common practice to feed thematerial to the uppermost hearth by means of a .chute passing throughthe top of the furnace and having a device serving to prevent the escapeof any substantial amount of furnace gases through the chute. As alreadydescribed the material would immediately be worked outwardly and leavebare a part of the hearth bounded I at its outside by a more or lessdefinite line in the general form of a spiral gradually increasing indistance from the center of the hearth until it reached the circle ofdrop holes at the periphery of the hearth.

According to the present invention it is proposed to distribute thematerial fed into the uppermost compartment of the furnace over anannular area of the uppermost hearth, concentric with the hearth itself,so that the material will be spread over the hearth with substantialuniformity and substantially all of the hearth surface will be utilized.In carryin out the invention in connection with a furnace (Figs. 1 and2) of which uppermost hearthhas outlet openings at its periphery, thematerial is introduced through a chute 28 under control of a weightedflapor gate 2| which acts to prevent the escape of gases. From the chutethe material drops on a horizontal support .or platform 22 just belowthe lower end of the chute and mounted to turn about the axis of theshaft I1 and having circular outer edge 23 of which the center lies insaid axis. .Preferably the support 22 is connected to said shaft torotate there with. The lower portions of the outer and inner walls ofthe chute 20 may be considered parts of the spiral blade andconsequently the ends of the spiral blade 24 may be described as overlpping. In order to distribute properly on the hearth material suppliedto said support, it is necessary to discharge material on the supportgradually over said circular edge thus depositing'it in an annular areaon the hearth I 3. Such an ,efiect may be produced by means of agenerally spiral fixed unloading blade 24 (Fig. 2) in the general formof a spiral starting as substantially a continuation of the inner wallof the lower end of the chute and gradually increasing in distance fromthe axis of the shaft ll until it reasonable uniformity on the uppersurface of the next lower hearth.

Obviously the shape of the blade as a -whole may be varied withoutchanging its operation,

the essential feature of the blade being that its material-engaging facemust be suitably shaped to produce the desired action. In order to feedthe material smoothly from the chute 20 to the support 22 it isdesirable to bring the lower end of the chute close to the support andto omit the discharge side of the lower end of the chute inside thefurnace so that the material is free to be removed by the rotatingsupport. Preferably also the inner end of the unloading bladeconstitutes an extension of the inner wall of the chute at its lower endand the outer end of the blade is attached to the outer wall of thechute. The construction just described is shown very clearly in Figs. 2and 3. It will be evident that the unloading blade serves as a cam.

The present invention may be applied to mul- 'tiple hearth furnaces oftypes heretofore in use without any substantial change in the generalfurnace construction. In order to maintain the same working conditionsin the compartment above the uppermost hearth of the furnace the tralportion having at its bottom an opening of somewhat greater diameterthan the diameter of the support 22, as illustrated in Figs. 1 and 3.

The top l2 proper may be provided at its cenin diameter from the uppersurface of the hearth [2 to the lower surface thereof. The opening inthe hearth may receive a tapered flange 25 of a ring 26 of suitablematter such as metal, said ring 28 also being provided with a flange 21to engage the upper surface of the top l2 around the central opening.The ring 26v may be turned in above the flange 21 so as to present atits top a horizontal seat to support a cap 28 which carries part of thegas seal around the shaft ll and.also carries a chute 20 which maybemade integral therewith.

In this embodiment of the invention the support 22 is in the form of anannulus resting on an upwardly projecting flange of the shaft I'I, thusrequiring the lower end of the chute 20 to be brought close to the shaftl'l. According to this arrangement the chute 20 may be inclined inwardlyto feed the material to the top of the support 22. Besides beingattached to the lower end of the chute 20 the unloading blade 24 may besupported by suitable means from the cap 28 a at points remote from thechute.

As illustrated in Fig. l the uppermost compartment of the furnacecommunicates with a duct or flue 30 which may be used for supplying airif the furnace be of the down-draft type, or if the furnace be of theup-draft type. the gases may be withdrawn through duct 30 under theinter with a tapered circular opening decreasing fiuence of draftproducing means such as a stack- (not shown). It will be evident thatthe arrangemen-t of drop openingsv M around the periphery of the hearthl3 serves to assist in con-' trolling the gas flow and to render suchflow more uniform than with a. central drop opening in the uppermosthearth.

The support 22 of Fig. l must be of substantial width and as thematerial fed to said support must be passed over the circular outer edgeof said support, it will ordinarily be deposited on the hearth. l3 at a,substantial distance from the shaft 11. However, shown in Fig. 4, usemay be made of an annular support 2211 spaced from the shaft I! so thatthe material deposited on the support 22a will be fed over the circularinner edge thereof, thus enabling the material to be deposited on thehearth l3 near the shaft H. The support 22a may be supported by suitablearms 3| projecting from the shaft I1. With this arrangement of thesupport 22a the opening in the furnace top I2 must, as shown in Fig. 4,be larger than in Fig. 1, thus enabling the chute 20a to be positionedfarther from the shaft I1 and to be ar-- ranged vertically. Asillustrated in Fig. 4 the cap 280, may be substantially flat andsupported at its periphery on a ring 26a.

with the arrangement Due to the fact that the material is dischargedover the inner edge of the support 220., the unloading plate 24a must bechanged accordingly from the form shown in Fig. 2 so as to force thematerial inwardly during rotation of the support or plate 2211, asindicated in Fig. 5. In this form of the apparatus the flat cap may berelatively close to the support 22a and the unloading blade engages thelower side of the cap and is attached thereto. A portion of the outerend of the blade 24a may be considered as the outer wall of the chutebeneath the cap and an extension 32 of the. inner end of the bladeproper may serve as the inner wall of the chute, there being no front orrear wall. 2

Where the material is dropped to the hearth l2 over an area so close tothe shaft H, as shown in Figs. 1 and 4, there is very little danger ofthe material entering the discharge flue 30. However, any such tendencymight be met by providing a dwell portion, for example in the form of acircular arc, in the part of the unloading blade nearest said flue 30.

In Figs; 6 and 7 there is illustrated an application of the invention toa furnace in which the.

uppermost hearth l3b has a central drop opening Nb and the rabblingdevice above the hearth l3b has its blades arranged so as to feed thematerial towards the central drop opening. In the form illustrated inFig. 6, the usual top of the furnace may be omitted and replaced by acap 28b extending completely across the furnace and having at one pointalong its periphery, a chute 20b through which material can drop toloading blade 24b may engage the lower surface of the cap 281) and beattached directly thereto, the outer end of the unloading blade beinglocated beneath the outer side of the chute and the other end may belocated beneath the inner side of the chute or the charging opening. Inthis form the chute does not extend below the cap, but the blades areconnnected by a rear 1 support 22b immediately in front of the entranceof flue 30b and may pass into the same. However, such an effect-may beprevented by forming the blade 24b with a dwell portion 24c opposite theflue 29b. Such dwell portion 240 may be in the form of an arc of acircle aboutthe axis of the shaft as a center.

The design of furnace shown in Figs. 6 and 7 is more adaptable torelatively small units of which the diameter is in the neighborhood ofeight to ten feet. I

It will-be evident that by depositing the mater'ial to be treated, in anarc of a circle on the uppermost hearth in accordance with the presentinvention, the material will be distributed substantiallyuniformly overthe surface of said hearth. In this way substantially the whole uppersurface of the uppermost hearth may be utilized, thus producing moreuniform treatment and having the effect of increasing the capacity asupport 22b, preferably annular in form, positioned near the innersurface of the peripheral wall of the furnace.

The support 22b may be sustained by means of arms'3lb which maybeintegral therewith, projecting from the shaft I! to the support at anyconvenient intervals around the shaft. In view of the omission of theusual thick top of the furnace, the cap 28b may rest on the top of theperipheral wall of the furnace and the support 22b may be located ratherclose to the cap. It

should be understood that the support 22b and arm 3Ib when formedintegrally may be split for convenience in assembly (Fig. 7). The unofthe furnace for drying and burning.

It should be understood that various changes may be made and thatcertain features may be 'used without others, without departing from thetrue scope and spirit of the invention. i

What I claim is:

1. In a furnace having a central vertical rotary shaft, a horizontallyarranged annular hearth providing a central opening in which said shaftis located, gravity outlet means arranged at one edge of said annularhearth and rabbling means carried by said shaft to work material on saidhearth to said gravity outlet means; means for feeding material to saidhearth to cause substantially uniform distribution of said materialthereover by said rabbling means, comprising a support rotating withsaid shaft and having a generally circular discharge edge adjacent tothe edge of the hearth remote from said outlet means, blade means in thegeneral form of a spiral with overlapping ends above said support andheld against rotation therewith, one of said overlapping ends beingadjacent to said circular edge of the support and the other end beingremot therefrom, and means for supplying material to the space betweensaid overlapping ends.

2. The combination as set forth in claim 1, in which the location of thegravity outlet means is at the outer edge of the hearth and thecircuwhich the location of the gravity outlet means is at the outer edgeof the hearth and the circular edge of the support is the inner edgethereof and is adjacent to the inner edge of said hearth.

5. The combination as set forth in claim 1, in

8. The combination as set forth in claim 1, in

which the end edge of the end of said blade means remote from thecircular edge of the support is connected by a generally radial wall tothe other end portion of said blade means.

9. The combination as set forth in claim 1, in which the furnace has alateral gas outlet above said hearth, the location of the gravity outletmeans is at the inner edge of the hearth, the circular edge of thesupport is its outer edge, and the blade means is located withoverlapping ends at a side of the furnace remote from said gas outletand has a generally circular portion concentric with said shaft andlocated adjacent said gas outlet to avoid discharge of the materialthrough said gas outlet.

WARREN S. MARTIN.

